Semiconductor nanoparticles, method of producing the semiconductor nanoparticles, and light-emitting device

ABSTRACT

Semiconductor nanoparticles including Ag, In, Ga, and S are provided. In the semiconductor nanoparticles, a ratio of a number of Ga atoms to a total number of In and Ga atoms is 0.95 or less. The semiconductor nanoparticles emit light having an emission peak with a wavelength in a range of from 500 nm to less than 590 nm, and a half bandwidth of 70 nm or less, and have an average particle diameter of 10 nm or less.

BACKGROUND Technical Field

The present invention relates to semiconductor nanoparticles, a methodof producing the semiconductor nanoparticles, and a light-emittingdevice.

Description of the Related Art

Semiconductor particles with a particle diameter of, for example, 10 nmor less are known to exhibit a quantum size effect, and suchnanoparticles are referred to as “quantum dots” (also referred to as“semiconductor quantum dots”). The quantum size effect is a phenomenonwhere a valence band and a conduction band, each of which is regarded ascontinuous in bulk particles, become discrete in nanoparticles, and thebandgap energy varies in accordance with their particle diameter.

Quantum dots can absorb light and change the wavelength of the lightcorresponding to the bandgap energy. Thus, white light-emitting devicesusing quantum dots are proposed (e.g., refer to Japanese UnexaminedPatent Application Publications No. 2012-212862 and No. 2010-177656).More specifically, light emitted from a light-emitting diode (LED) chipis partially absorbed by quantum dots, and the emission from the quantumdots and the light from the LED chip are mixed to produce white light.In these patent application documents, use of binary quantum dots ofGroup 12-Group 16 materials, such as CdSe or CdTe, or Group 14-Group 16materials, such as PbS or PbSe, is proposed. Also, as ternarysemiconductor nanoparticles that exhibit a band edge emission and thatcan have a composition with low toxicity, tellurium compoundnanoparticles (e.g., Japanese Patent Application Publication No.2017-014476) and sulfide nanoparticles (e.g., Japanese PatentApplication Publication No. 2017-025201) are proposed.

SUMMARY Problems to be solved by the Invention

However, the semiconductor nanoparticles described in Japanese PatentApplication Publications No. 2017-014476 and No. 2017-025201 have a peakemission wavelength at relatively long wavelengths. Thus, an aspect ofthe present invention is directed to semiconductor nanoparticles thatexhibit a band edge emission, and have a peak emission wavelength atshort wavelengths.

Means for Solving the Problem

A first aspect is directed to semiconductor nanoparticles containing Ag,In, Ga, and S, in which the ratio of the number of Ga atoms to the totalnumber of In and Ga atoms is from 0.95 or less, emitting light having anemission peak with a wavelength in a range of from 500 nm to less than590 nm and a half bandwidth of 70 nm or less upon irradiation withlight, and having an average particle diameter of 10 nm or less.

A second aspect is directed to a method of producing semiconductornanoparticles including preparing a mixture containing silver acetate,indium acetylacetonate, gallium acetylacetonate, a sulfur source, and anorganic solvent; and heat-treating the mixture.

A third aspect is directed to a light-emitting device including a lightconversion member containing the semiconductor nanoparticles, and asemiconductor light-emitting element.

Effect of the invention

An aspect of the present invention may provide semiconductornanoparticles that exhibit a band edge emission, and have a peakemission wavelength at short wavelengths.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing emission spectra of semiconductornanoparticles.

FIG. 2 is a graph showing absorption spectra of semiconductornanoparticles.

FIG. 3 is a graph showing an XRD pattern of semiconductor nanoparticlesaccording to Example 4.

FIG. 4 is a graph showing emission spectra of semiconductornanoparticles.

FIG. 5 is a graph showing absorption spectra of semiconductornanoparticles.

FIG. 6 is a graph showing emission spectra of core-shell semiconductornanoparticles according to Examples 12 to 16.

FIG. 7 is a graph showing emission spectra of core-shell semiconductornanoparticles according to Examples 17 and 18.

FIG. 8 is a graph showing an emission spectrum of TOP-modifiedcore-shell semiconductor nanoparticles according to Example 19.

DETAILED DESCRIPTION

Embodiments according to the present invention will now be described.However, the embodiments described below are examples of thesemiconductor nanoparticles, the method of producing the semiconductornanoparticles, and the light-emitting device for embodying the technicalconcept of the present invention, and the present invention is notlimited to the semiconductor nanoparticles, the production method, andthe light-emitting device described below. As used herein, the term“step” means not only an independent step but also a step which cannotbe clearly distinguished from the other steps but that can achieve theintended object. For the amount of each component contained in acomposition, when a plurality of substances corresponding to thecomponent are present in the composition, the amount of the componentmeans the total amount of the corresponding substances present in thecomposition unless otherwise specified.

Semiconductor Nanoparticles

The semiconductor nanoparticles, which is a first embodiment, containssilver (Ag), indium (In), gallium (Ga), and sulfur (S). Thesemiconductor nanoparticles have a ratio of the number of Ga atoms tothe total number of In and Ga atoms (Ga/(Ga+In)) of 0.95 or less. Thesemiconductor nanoparticles emit light having a peak emission with awavelength in the range of from 500 nm to less than 590 nm, and aspectral half bandwidth of 70 nm or less upon irradiation with light.The semiconductor nanoparticles have an average particle diameter of 10nm or less.

The semiconductor nanoparticles containing Ag, In, Ga, and S, and havinga ratio of the number of Ga atoms to the total number of In and Ga atomsin the predetermined range exhibit a band edge emission having a peakemission in the range of from 500 nm to less than 590 nm, which is alonger wavelength than excitation light, and is in the visible region.

The semiconductor nanoparticles may have at least one crystal structureselected from the group consisting of tetragonal crystal, hexagonalcrystal, and orthorhombic crystal. Semiconductor nanoparticlescontaining Ag, In, and S, and having a tetragonal, hexagonal, ororthorhombic crystal structure are typically described in, for example,literature as represented by the composition formula: AgInS₂.Semiconductor nanoparticles according to the present embodiment may beregarded as the semiconductor nanoparticles where, for example, In,which is a Group 13 element, is partially substituted by Ga, which isanother Group 13 element. In other words, the semiconductornanoparticles have a composition represented by, for example, Ag-In-Ga-Sor Ag(In, Ga)S₂.

The semiconductor nanoparticles represented by, for example, thecomposition formula: Ag-In-Ga-Se with a hexagonal crystal structure iswurtzite, and those with a tetragonal crystal structure is chalcopyrite.The crystal structure of the semiconductor nanoparticles is identifiedby, for example, measuring the XRD pattern obtained through X-raydiffraction (XRD) analysis. Specifically, the XRD pattern obtained fromthe semiconductor nanoparticles is compared with known XRD patterns ofsemiconductor nanoparticles represented by the composition: AgInSe₂ orwith the XRD patterns obtained through simulations using the crystalstructure parameters. If the pattern of the semiconductor nanoparticlescoincides with a pattern among the known patterns and the simulatedpatterns, the semiconductor nanoparticles have a crystal structure ofthe coincided pattern.

An aggregate of the semiconductor nanoparticles may be a mix of thesemiconductor nanoparticles with different crystal structures. In thiscase, peaks attributable to a plurality of crystal structures areobserved in the XRD pattern.

The semiconductor nanoparticles may be essentially composed of Ag, In,Ga, and S. The term “essentially” is used herein on the understandingthat elements other than Ag, In, Ga, Se, and S and attributable to, forexample, mixed-in impurities can unavoidably be contained.

The ratio of the number of Ga atoms to the total number of In and Gaatoms, or Ga/(Ga+In), (hereinafter also referred to as “Ga ratio”) maybe 0.95 or less, and more preferably from 0.2 to 0.9.

The ratio of the number of Ag atoms to the total number of Ag, In, andGa atoms, or Ag/(Ag+In+Ga), (hereinafter also referred to as “Ag ratio”)may be from 0.05 to 0.55.

Ag ratio can be from 0.3 to 0.55, and Ga ratio may be from 0.5 to 0.9,and preferably Ag ratio may be from 0.35 to 0.53, and Ga ratio can befrom 0.52 to 0.86.

Ga ratio may be from 0.2 to 0.9, and Ga ratio+2×Ag ratio may be from 1.2to 1.7, and preferably Ga ratio may be from 0.2 to 0.9, Ag ratio may befrom 0.3 to 0.55, and Ga ratio+2×Ag ratio may be from 1.2 to 1.7.

Ag ratio may be from 0.05 to 0.27, and Ga ratio may be from 0.25 to0.75. Preferably Ag ratio may be from 0.06 to 0.27, and Ga ratio may befrom 0.26 to 0.73.

Ga ratio may be from 0.2 to 0.8, and Ga ratio+2×Ag ratio may be from 0.6to 1, and preferably Ga ratio may be from 0.2 to 0.8, Ag ratio may befrom 0.05 to 0.4, and Ga ratio+2×Ag ratio may be from 0.6 to 1.

The ratio of the number of S atoms to the total number of Ag, In, and Gaatoms, or S/(Ag+In+Ga), (hereinafter also referred to as “S ratio”) maybe, for example, from 0.6 to 1.6.

The composition of the semiconductor nanoparticles may be identified byusing, for example, X-ray fluorescence (XRF) analysis. Ga ratio orGa/(Ga+In), Ag ratio or Ag/(Ag+In+Ga), and S ratio or S/(Ag+In+Ga) arecalculated based on the composition determined by this method.

The semiconductor nanoparticles have an average particle diameter of 10nm or less. The average particle diameter may be, for example, less than10 nm, and preferably 5 nm or less. With an average particle diameterexceeding 10 nm, the quantum size effect cannot be easily obtained, andthe band edge emission cannot be easily exhibited. The lower limit ofthe average particle diameter is, for example, 1 nm.

The particle diameter of the semiconductor nanoparticles can bedetermined from, for example, a TEM image captured using a transmissionelectron microscope (TEM). Specifically, the particle diameter of aparticle observed in a TEM image is defined as the length of the longestline segment among the line segments connecting two points on thecircumference of the particle and passing through the particle.

However, for a rod-shaped particle, the length of the short axis isdefined as the particle diameter. A rod-shaped particle is a particlehaving a short axis and a long axis orthogonal to the short axis, andthe ratio of the long axis to the short axis is greater than 1.2 in aTEM image. Examples of the rod-shaped particles include tetragonal(including rectangular), elliptical, and polygonal particles observed inan TEM image. The rod-shaped particles may have, for example, acircular, elliptical, or polygonal cross-section, which is a planeorthogonal to the long axis. Specifically, for a rod-shaped particlewith an elliptical cross-section, the length of the long axis is thelongest line segment among the line segments connecting two points onthe circumference of the particle. For a rod-shaped particle with arectangular or polygonal cross-section, the length of the long axis isthe longest line segment among the line segments parallel to the longestside among the sides defining the perimeter and connecting two points onthe perimeter of the particle. The length of the short axis is thelongest line segment among the line segments connecting two points onthe perimeter of the particle, and orthogonal to the line segmentdefining the length of the long axis.

The average particle diameter of the semiconductor nanoparticles isdetermined by measuring the particle diameters of all the measurableparticles observed in a TEM image captured with 50,000 to 150,000×magnification, and averaging the particle diameters. The term“measurable” particles as used herein refers to particles whose entireimages are observable in a TEM image. Thus, in a TEM image, particlespartially not in the captured site and observed as partially cut-outparticles are not measurable. When a TEM image contains 100 or moremeasurable particles, their average particle diameter is obtained usingthe single TEM image. When a TEM image contains less than 100 measurableparticles, another TEM image is captured in a different site of theparticles, and an average particle diameter is obtained by measuring andaveraging the particle diameters of 100 or more measurable particlesusing the two or more TEM images.

The semiconductor nanoparticles containing Ag, In, Ga, and S, and havingthe ratio of the number of Ga atoms to the total number of In and Gaatoms in a predetermined range may exhibit a band edge emission. Thesemiconductor nanoparticles emit light with a peak emission wavelengthin the range of from 500 nm to less than 590 nm upon irradiation oflight having a peak around 365 nm. The peak emission wavelength may be,for example, from 500 nm to 580 nm, from 500 nm to 575 nm, or from 505nm to less than 575, or, from 570 nm to 585 nm or from 575 nm to 580 nm.The peak emission may have a spectral half bandwidth of, for example, 70nm or less, 60 nm or less, 55 nm or less, or 50 nm or less. The lowerlimit of the half bandwidth may be, for example, 10 nm or more, or 20 nmor more.

The semiconductor nanoparticles may show other emissions, for example,defect emission as well as band edge emission. A typical defect emissionhas a long emission lifetime and a broad spectrum, and has a peak atlonger wavelengths than band edge emission. When both band edge emissionand defect emission are exhibited, the intensity of the band edgeemission is preferably greater than the intensity of the defectemission.

The semiconductor nanoparticles may exhibit a band edge emission with apeak appearing in a different position by changing the shape and/or theaverage particle diameter, in particular the average particle diameter.For example, the semiconductor nanoparticles having a smaller averageparticle diameter have greater band gap energy because of the quantumsize effect, and thus may exhibit a band edge emission with a peakwavelength shifted at shorter wavelengths.

The semiconductor nanoparticles may exhibit a band edge emission with apeak appearing in a different position by changing the composition ofthe semiconductor nanoparticles. For example, with a greater Ga ratio,the semiconductor nanoparticles may exhibit a band edge emission with apeak wavelength shifted at shorter wavelengths.

The semiconductor nanoparticles preferably show an absorption spectrumwith an exciton peak. An exciton peak is a peak resulting from excitonformation. Thus, the semiconductor nanoparticles with an exciton peakappearing in the absorption spectrum are suitable for a band edgeemission with a small particle diameter distribution, and less crystaldefect. The semiconductor nanoparticles having a sharper exciton peakcontain more particles with a uniform particle diameter and less crystaldefect in its aggregate of the particles. Thus, a sharp exciton peakseemingly indicates a narrower emission half bandwidth, and improvedemission efficiency. The semiconductor nanoparticles according to thepresent embodiment show an absorption spectrum with an exciton peak inthe range of, for example, from 450 nm to less than 590 nm.

The semiconductor nanoparticles may have its surface modified with asurface modifier. A surface modifier, for example, stabilizes thesemiconductor nanoparticles to prevent aggregation or growth of theparticles, and/or improves dispersibility of the particles in a solvent.

Examples of the surface modifier include nitrogen-containing compoundshaving a hydrocarbon group with a carbon number of from 4 to 20,sulfur-containing compounds having a hydrocarbon group with a carbonnumber of from 4 to 20, and oxygen-containing compounds having ahydrocarbon group with a carbon number of from 4 to 20. Examples of thehydrocarbon group with a carbon number of from 4 to 20 include saturatedaliphatic hydrocarbon groups, such as n-butyl, isobutyl, n-pentyl,n-hexyl, octyl, decyl, dodecyl, hexadecyl, and octadecyl; unsaturatedaliphatic hydrocarbon groups, such as oleyl; alicyclic hydrocarbongroups, such as cyclopentyl and cyclohexyl; and aromatic hydrocarbongroups, such as phenyl, benzyl, naphthyl, and naphthylmethyl. Of these,saturated aliphatic hydrocarbon groups and unsaturated aliphatichydrocarbon groups are preferable. Examples of the nitrogen-containingcompounds include amines and amides. Examples of the sulfur-containingcompound include thiols. Examples of the oxygen-containing compoundinclude fatty acids.

Preferably, the surface modifier is a nitrogen-containing compoundhaving a hydrocarbon group with a carbon number of from 4 to 20.Examples of such nitrogen-containing compound include alkylamines, suchas n-butylamine, isobutylamine, n-pentylamine, n-hexylamine, octylamine,decylamine, dodecylamine, hexadecylamine, and octadecylamine, andalkenyl amines, such as oleylamine.

Also preferably, the surface modifier is a sulfur-containing compoundhaving a hydrocarbon group with a carbon number of from 4 to 20.Examples of such sulfur-containing compounds include alkyl thiols, suchas n-butane thiol, isobutane thiol, n-pentane thiol, n-hexane thiol,octane thiol, decane thiol, dodecane thiol, hexadecane thiol, andoctadecane thiol.

Two or more different surface modifiers may be used in combination. Forexample, a single compound selected from the above examples of thenitrogen-containing compound (e.g., oleylamine) and a single compoundselected from the above examples of the sulfur-containing compound(e.g., dodecane thiol) may be used in combination.

Method of Producing Semiconductor Nanoparticles

The method of producing semiconductor nanoparticles according to asecond embodiment includes preparing a mixture containing a salt ofsilver, a salt of indium, a salt of gallium, a source of sulfur, and anorganic solvent, and heat-treating the prepared mixture. Preferably, amixture containing silver acetate, indium acetylacetonate, galliumacetylacetonate, sulfur or thiourea serving as a sulfur source, and anorganic solvent is prepared.

The mixture can be prepared by adding a salt of silver, a salt ofindium, a salt of gallium, and a source of sulfur to an organic solvent,and mixing them. The ratio of Ag, In, Ga, and S in the mixture isselected as appropriate in accordance with the target composition. Forexample, the molar ratio of Ga to the total molar amount of In and Ga isfrom 0.2 to 0.9. Also, for example, the molar ratio of Ag to the totalmolar amount of Ag, In, and Ga is from 0.05 to 0.55. Also, for example,the molar ratio of S to the total molar amount of Ag, In, and Ga is from0.6 to 1.6.

Examples of the organic solvent include amines having a hydrocarbongroup with a carbon number of from 4 to 20, in particular, alkylamine oralkenylamine with a carbon number of from 4 to 20, thiols having ahydrocarbon group with a carbon number of from 4 to 20, in particular,alkylthiol or alkenylthiol with a carbon number of from 4 to 20, andphosphines having a hydrocarbon group with a carbon number of from 4 to20, in particular, alkylphosphine or alkenylphosphine with a carbonnumber of from 4 to 20. These organic solvents can eventuallysurface-modify the resulting semiconductor nanoparticles. The organicsolvent may be formed from two or more of these organic solvents incombination. In particular, a mixed solvent containing at least oneselected from thiols having a hydrocarbon group with a carbon number offrom 4 to 20, and at least one selected from amines having a hydrocarbongroup with a carbon number of from 4 to 20 may be used in combination.These organic solvents may also be mixed with other organic solvents.

In the method of producing semiconductor nanoparticles, the mixture isheat-treated to produce semiconductor nanoparticles in an organicsolvent. The temperature at which the mixture is heat-treated is, forexample, from 230° C. to 310° C., preferably above 260° C. to 310° C.,and more preferably from 290° C. to 310° C. The duration of the heattreatment is, for example, from 5 minutes to 20 minutes, and preferablyfrom 5 minutes to 15 minutes. The mixture may be heat-treated at two ormore different temperatures. For example, the mixture may beheat-treated at a temperature of from 30° C. to 155° C. for from 1 minto 15 min, and then at a temperature of from 230° C. to 310° C. for from5 min to 20 min.

The heat treatment atmosphere is an inert atmosphere, and particularlypreferably an argon atmosphere or a nitrogen atmosphere. An inertatmosphere can reduce or prevent production of an oxide, or aby-product, and oxidation of the surface of the semiconductornanoparticles.

Upon completion of the production of the semiconductor nanoparticles,the resultant semiconductor nanoparticles may be separated from theorganic solvent, which has undergone treatment, and may be furtherpurified as appropriate. The separation after the production may becarried out, for example, by centrifuging the organic solvent containingthe nanoparticles, and collecting the supernatant liquid containing thenanoparticles. The purification may be carried out by, for example,adding an organic solvent to the supernatant liquid, centrifuging themixture, and collecting the precipitate, or the semiconductornanoparticles. The semiconductor nanoparticles may also be collected byvaporizing the supernatant liquid. The collected precipitate may bedried, for example, through vacuum deairing or natural drying, or acombination of vacuum deairing and natural drying. Natural drying may becarried out, for example, by leaving the precipitate as it is inatmospheric air at normal temperature and at normal pressure for 20hours or more, for example, about 30 hours.

The collected precipitate may be dispersed in an organic solvent. Thepurification (addition of alcohol and centrifugation) may be repeatedmultiple times as appropriate. The alcohol to be used for purificationmay be a lower alcohol with a carbon number of 1 to 4, such as methanol,ethanol, or n-propyl alcohol. When the precipitate is dispersed in anorganic solvent, for example, a halogen solvent, such as chloroform, ora hydrocarbon solvent, such as toluene, cyclohexane, hexane, pentane, oroctane, may be used as the organic solvent.

Core-Shell Semiconductor Nanoparticles

The semiconductor nanoparticles may be core-shell semiconductornanoparticles including a core selected from at least one of thesemiconductor nanoparticles according to the first embodiment and thesemiconductor nanoparticles produced by the method according to thesecond embodiment, and a shell forming a heterojunction with the core,and having a greater band gap energy than the core. The semiconductornanoparticles having a core-shell structure can exhibit a furthergreater band edge emission.

The shell is a semiconductor material preferably essentially composed ofGroup 13 and Group 16 elements. Examples of Group 13 elements include B,Al, Ga, In, and Tl, and examples of Group 16 elements include O, S, Se,Te, and Po.

The shell may also be a semiconductor material essentially composed ofGroup 1, Group 13, and Group 16 elements. Containing a Group 1 elementin addition to Group 13 and Group 16 elements tends to reduce defectemission. Examples of Group 1 element include Li, Na, K, Rb, and Cs, andLi, which has a closer ion radius to Al, is preferable.

Although the band gap energy of the core semiconductor varies inaccordance with its composition, Group 11-Group 13-Group 16 ternarysemiconductors typically have a band gap energy of from 1.0 eV to 3.5eV. In particular, a semiconductor with a composition of Ag-In-Ga-S hasa band gap energy of from 2.0 eV to 2.5 eV, and thus the shell mayselect, for example, its composition in accordance with the band gapenergy of the core semiconductor. When, for example, the composition ofthe shell is predetermined, the core semiconductor may be designed tohave a band gap energy smaller than the shell.

Specifically, the shell may have a band gap energy of, for example, from2.0 eV to 5.0 eV, in particular from 2.5 eV to 5.0 eV. The shell mayhave a greater band gap energy than the core by, for example, from about0.1 eV to about 3.0 eV, particularly, from about 0.3 eV to about 3.0 eV,and more particularly from about 0.5 eV to about 1.0 eV. When thedifference in band gap energy between the shell and the core is small,the ratio of emission other than the band edge emission from the corecan be greater, and this may reduce the ratio of the band edge emission.

The band gap energy of the core semiconductor and the band gap energy ofthe shell semiconductor are preferably selected to form a type-I bandalignment where the core band gap energy exists between the shell bandgap energy in heterojunction of the core and the shell. The type-I bandalignment enables further satisfactory band edge emission from the core.In the type-I alignment, at least 0.1 eV barrier is preferably formedbetween the core band gap and the shell band gap, and, in particular,0.2 eV or more, more particularly 0.3 eV or more barrier may be formed.The upper limit of the barrier is, for example, 1.8 eV or less, andparticularly 1.1 eV or less. When the barrier is small, the ratio ofemission other than the band edge emission from the core can be greater,and this can reduce the ratio of the band edge emission.

The shell may contain Ga, or a Group 13 element, and S, or a Group 16element. The semiconductors containing Ga and S tend to have greaterband gap energy than the Group 11-Group 13-Group 16 ternarysemiconductors.

The shell semiconductor may have a crystal system in accord with thecrystal system of the core semiconductor. Also, the shell semiconductormay have a lattice constant equal or close to the lattice constant ofthe core semiconductor. A shell formed from a semiconductor with acrystal system in accord with the crystal system of the core, and alattice constant close to the core lattice constant (including itsmultiples close to the core lattice constant) may cover the periphery ofthe core appropriately. For example, the Group 11-Group 13-Group 16ternary semiconductors typically have a tetragonal crystal system, andexamples of the crystal system in accord with tetragonal crystal includetetragonal crystal, and orthorhombic crystal. An Ag-In-Ga-Ssemiconductor with a tetragonal crystal system has a lattice constant of5.828 Å, 5.828 Å, or 11.19 Å. Preferably, the shell covering this corehas a tetragonal crystal or cubic crystal system, and a lattice constantor its multiples close to the lattice constant of Ag-In-Ga-S. Or, theshell may be amorphous.

Whether an amorphous shell is formed can be checked by observing thecore-shell semiconductor nanoparticles using a high-angle annulardark-field scanning transmission electron microscopy (HAADF-STEM). AnHAADF-STEM shows an image with a regular pattern for a substance with aregular structure like a crystal substance, and an image with no regularpattern for a substance with no regular structure like an amorphoussubstance. Thus, an amorphous shell can be observed as an area clearlydistinct from the core shown with an image of a regular pattern (with acrystal structure such as a tetragonal crystal system as describedabove).

When the core is formed from Ag-In-Ga-S and the shell is formed fromGaS, the shell may be shown as a darker area than the core area in animage obtained through an HAADF-STEM because Ga is a lighter elementthan Ag and In.

Whether an amorphous shell is formed can also be checked by observingthe core-shell structured semiconductor nanoparticles through ahigh-resolution transmission electron microscope (HRTEM). In the imageobtained through an HRTEM, a crystal lattice image is observed for thecore area (an image with a regular pattern), and the shell area is notobserved as a crystal lattice image, but as an area of mere black andwhite contrast with no regular pattern.

When the shell is a semiconductor containing a combination of Ga and S,or a combination of Group 13 and Group 16 elements, the combination ofGa and S may take a form of gallium sulfide. The gallium sulfide formingthe shell may not have a stoichiometric composition (Ga₂S₃). In thissense, gallium sulfide is herein represented by formula GaS_(x) (where xis not limited to an integer but any number, for example, from 0.8 to1.5).

Gallium sulfide has band gap energy of from about 2.5 eV to about 2.6eV, and gallium sulfide with a tetragonal crystal system has a latticeconstant of 5.215 Å. However, the crystal system and others describedabove are all reported values, and actual core-shell semiconductornanoparticles may not have a shell satisfying these values. Galliumsulfide, which has large band gap energy, is preferably used as a shellsemiconductor. A gallium sulfide shell may exhibit a further strong bandedge emission.

When the shell is a semiconductor containing a combination of Li, Ga,and S, or a combination of Group 1, Group 13, and Group 16 elements, thecombination may take a form of, for example, gallium lithium sulfide.The gallium lithium sulfide may not have a stoichiometric composition(e.g., LiGaS₂). For example, the composition may be represented byLiGaS_(x) (where x is not limited to an integer but any number, forexample, from 1.1 to 2). Also, for example, the gallium sulfide may beamorphous where Li is solid-solubilized. The molar ratio of Li to Ga(Li/Ga) in the shell may be, for example, from 1/20 to 4, or from 1/10to 2.

Gallium lithium sulfide has relatively large band gap energy of about 4eV. This enables a further stronger band edge emission. Also, Li hasabout the same size of ion radius as Ag, which is contained in the core.Thus, for example, the shell can have a similar structure to the core.This is believed to compensate core surface defects, and furthereffectively suppress defect emission.

The core-shell semiconductor nanoparticles may have a shell surfacemodified with a surface modifier. Specific examples of the surfacemodifier include phosphorus-containing compounds having a negativeoxidation number (hereinafter also referred to as “specific modifier”)in addition to the nitrogen-containing compounds having a hydrocarbongroup with a carbon number of from 4 to 20, the sulfur-containingcompounds having a hydrocarbon group with a carbon number of from 4 to20, and the oxygen-containing compounds having a hydrocarbon group witha carbon number of from 4 to 20 described above. With the shell surfacemodifier containing a specific modifier, the core-shell semiconductornanoparticles may exhibit a band edge emission with an improved quantumyield.

The specific modifier contains P, or Group 15 element, having a negativeoxidation number. The oxidation number of P becomes −1 when, forexample, a hydrogen atom or an alkyl group binds to P, and becomes +1when an oxygen atom binds through a single bond. The oxidation number ofP varies depending on how P is substituted. For example, P in trialkylphosphine and triaryl phosphine has an oxidation number of −3, and P intrialkyl phosphine oxide and triaryl phosphine oxide has an oxidationnumber of −1.

The specific modifier may contain, in addition to P with a negativeoxidation number, other Group 15 elements. Examples of the other Group15 elements include N, As, and Sb.

The specific modifier may be, for example, a phosphorus-containingcompound having a hydrocarbon group with a carbon number of from 4 to20. Examples of the hydrocarbon group with a carbon number of from 4 to20 include a linear or branched saturated aliphatic hydrocarbon group,such as n-butyl, isobutyl, n-pentyl, n-hexyl, octyl, ethylhexyl, decyl,dodecyl, tetradecyl, hexadecyl, and octadecyl; a linear or branchedunsaturated aliphatic hydrocarbon group, such as oleyl group; analicyclic hydrocarbon group, such as cyclopentyl and cyclohexyl; anaromatic hydrocarbon group, such as phenyl and naphthyl; and anarylalkyl group, such as benzyl and naphthyl methyl. Of these, asaturated aliphatic hydrocarbon group or an unsaturated aliphatichydrocarbon group is preferable. When the specific modifier has aplurality of hydrocarbon groups, they may be the same or different.

Examples of the specific modifier include tributylphosphine,triisobutylphosphine, triphenylphosphine, triphenylphosphine,trioctylphosphine, tris(ethylhexyl)phosphine, tridecylphosphine,tridodecylphosphine, tritetradecylphosphine, trihexadecylphosphine,trioctadecylphosphine, triphenylphosphine, tributylphosphine oxide,triisobutylphosphine oxide, triphenylphosphine oxide, trihexylphosphineoxide, trioctylphosphine oxide, tris(ethylhexyl)phosphine oxide,tridecylphosphine oxide, tridodecylphosphine oxide,tritetradecylphosphine oxide, trihexadecylphosphine oxide, trioctadecylphosphine oxide, and triphenyl phosphine oxide, and at least oneselected from the group consisting of these is preferable.

Method of producing core-shell semiconductor nanoparticles

The method of producing core-shell semiconductor nanoparticles includespreparing a dispersion containing the semiconductor nanoparticles,adding semiconductor raw materials to the dispersion of thesemiconductor nanoparticles, and forming a semiconductor layer on thesurfaces of the semiconductor nanoparticles. To cover the semiconductornanoparticles with a shell, the semiconductor nanoparticles is dispersedin an appropriate solvent to prepare a dispersion, and a semiconductorlayer to become a shell is formed in the dispersion. In a dispersionwhere the semiconductor nanoparticles are dispersed, light is notscattered, so that the dispersion is generally transparent (colored orcolorless). The solvent into which the semiconductor nanoparticles aredispersed can be any organic solvent (in particular, an organic solventwith high polarity, for example, an alcohol, such as ethanol) as inpreparing the semiconductor nanoparticles, and the organic solvent canbe a surface modifier or a solution containing a surface modifier. Forexample, the organic solvent can be a surface modifier described inrelation to the method of producing the semiconductor nanoparticles, orspecifically at least one selected from the nitrogen-containingcompounds having a hydrocarbon group with a carbon number of from 4 to20, or at least one selected from the sulfur-containing compounds havinga hydrocarbon group with a carbon number of from 4 to 20, or acombination of at least one selected from the nitrogen-containingcompounds having a hydrocarbon group with a carbon number of from 4 to20 and at least one selected from the sulfur-containing compounds havinga hydrocarbon group with a carbon number of from 4 to 20. Preferablespecific examples of the nitrogen-containing compounds includen-tetradecylamine and oleylamine, because they have a boiling pointexceeding 290° C., and are available with high purity. A specificexample of the sulfur-containing compound is dodecanethiol. Specificexamples of the organic solvent include oleylamine, n-tetradecylamine,dodecanethiol, and a combination of them.

The dispersion of the semiconductor nanoparticles may have a particleconcentration in the dispersion adjusted to, for example, from 5.0×10⁻⁷mol/L to 5.0×10⁻⁵ mol/L, in particular from 1.0×10⁻⁶ mol/L to 1.0×10⁻⁵mol/L. With a too small ratio of the particles in the dispersion, thepoor solvent makes it difficult to collect the product throughaggregation and precipitation process. With a too large ratio, the rateof fusion of core materials increases through Ostwald ripening orcollision, which tends to result in a broader particle diameterdistribution.

Shell Formation

The shell semiconductor layer is formed, for example, by adding a Group13 element-containing compound, and a Group 16 element in the form of asimple element or a Group 16 element-containing compound to thedispersion described above.

The Group 13 element-containing compound serves as a Group 13 elementsource, and examples include organic salts, inorganic salts, and organicmetal compounds of Group 13 elements. Specific examples of Group 13element-containing compounds include nitrate, acetate, sulfate,hydrochloride, sulfonate, and acetylacetonate complexes. Preferableexamples include organic salts, such as acetate, or organic metalcompounds, because organic salts and organic metal compounds are highlysoluble in an organic solvent, and can allow the reaction to proceedfurther uniformly.

The Group 16 element in the form of a simple element or the Group 16element-containing compound serves as a Group 16 element source. When,for example, sulfur (S), which is a Group 16 element, is used as ashell-forming element, sulfur in the form of a simple element such ashigh purity sulfur can be used, or a thiol, such as n-butanethiol,isobutanethiol, n-pentanethiol, n-hexanethiol, octanethiol, decanethiol,dodecanethiol, hexadecanethiol, or octadecanethiol; a disulfide, such asa dibenzyl sulfide; and a sulfur-containing compound, such as thioureaor a thiocarbonyl compound may be used.

When oxygen (O) is used as a Group 16 element for forming the shell,alcohol, ether, carboxylic acid, ketone, or a N-oxide compound may beused as the Group 16 element source. When selenium (Se) is used as aGroup 16 element for forming the shell, selenium in the form of a simpleelement, or selenide phosphine oxide, or a compound such as an organicselenium compound (dibenzyl diselenide or diphenyl diselenide) or ahydride may be used as the Group 16 element source. When tellurium (Te)is used as a Group 16 element for forming the shell, tellurium in theform of a simple element, telluride phosphine oxide, or a hydride may beused as a Group 16 element source.

The method of adding Group 13 and the Group 16 element sources to thedispersion is not particularly limited. For example, the Group 13 andGroup 16 element sources may be dispersed or dissolved in an organicsolvent to prepare a mixed solution, and the mixed solution may be addedportion-wise, for example, drop-wise to the dispersion. In this case,the mixed solution may be added at a rate of from 0.1 mL/h to 10 mL/h,in particular, from 1 mL/h to 5 mL/h. The mixed solution may be added toa heated dispersion. Specifically, for example, the temperature of thedispersion is raised to a peak temperature of from 200° C. to 310° C.,and when the peak temperature is reached, the mixed solution is addedportion-wise while the peak temperature is maintained, and then a shelllayer is formed by allowing the temperature to decrease (slow injectionmethod). The peak temperature may be maintained after the addition ofthe mixed solution as appropriate.

When the peak temperature is above the temperature described above, forexample, the surface modifier modifying the semiconductor nanoparticlesis fully removed, or a chemical reaction for forming the shell fullyproceeds. Thus, the formation of a semiconductor layer (shell) tends toproceed in a satisfactory manner. When the peak temperature is less thanthe above-described temperature, changes in properties of thesemiconductor nanoparticles tend to be reduced, and a good band edgeemission tends to be exhibited. The time period during which the peaktemperature is maintained can be from 1 min to 300 min, in particularfrom 10 min to 120 min in total from the starting of the addition of themixed solution. The time period during which the peak temperature ismaintained can be selected in relation to the peak temperature; the timeperiod for a low peak temperature can be made longer, and the timeperiod for a high peak temperature can be made shorter to form a goodshell layer. The temperature-increase and decrease rates are notparticularly limited. After the peak temperature is maintained for apredetermined time, the temperature may be decreased by, for example,stopping heating with a heating source (for example, an electricheater), and letting cool.

Alternatively, all the amounts of the Group 13 and Group 16 elementsources may be directly added to the dispersion. The dispersioncontaining the Group 13 and Group 16 element sources may then be heatedto form the shell semiconductor layer on the surfaces of thesemiconductor nanoparticles (heating up method). Specifically, thetemperature of the dispersion containing the Group 13 and Group 16element sources is, for example, gradually increased to a peaktemperature of from 200° C. to 310° C., maintained at the peaktemperature for from 1 min to 300 min, and then allowed to graduallydecrease. The rate at which the temperature is increased is, forexample, from 1° C/min to 50° C/min, and the rate at which thetemperature is decreased is, for example, from 1° C/min to 100° C/min.Or, the dispersion may be simply heated to reach a predetermined peaktemperature without particularly controlling the rate at which thetemperature is increased, and heating with a heating source may bestopped to allow cooling without particularly controlling the rate atwhich the temperature is decreased to a given rate. The advantage of thepeak temperature being in the range above is as described in the methodof adding the mixed solution (slow injection method).

The heating up method tends to produce core-shell semiconductornanoparticles that exhibit a stronger band edge emission than the casewhere the shell is formed by the slow injection method.

Regardless of any of the methods used to add the Group 13 and Group 16element sources, their initial ratio may be determined in accordancewith the stoichiometric composition ratio of the compound semiconductorcontaining Group 13 and Group 16 elements, but their initial ratio maynot necessarily follow the stoichiometric composition ratio. When theinitial ratio is not in correspondence with the stoichiometriccomposition ratio, the raw materials may be used excessively than thetarget amount of product of the shell. Or, for example, the ratio of theGroup 16 element source may be less than the stoichiometric compositionratio, or, for example, the initial ratio may be 1:1 (Group 13:Group16). For example, when an In source is used as the Group 13 elementsource and an S source is used as the Group 16 element source, theinitial ratio is preferably 1:1 instead of 1:1.5 (In:S), whichcorresponds to the composition formula: In₂S₃. Similarly, when a Gasource is used as the Group 13 element source and an S source is used asthe Group 16 element source, the initial ratio is preferably 1:1 insteadof 1:1.5 (Ga:S), which corresponds to the composition formula: Ga₂S₃.

To form a shell with a desired thickness on the semiconductornanoparticles in the dispersion, the initial amount is selected takingthe amount of the semiconductor nanoparticles in the dispersion intoaccount. For example, the initial amounts of the Group 13 and the Group16 element sources may be determined to produce 1 μmol to 10 mmol, inparticular, from 5 μmol to 1 mmol of a compound semiconductor containingGroup 13 and Group 16 elements with a stoichiometric compositionrelative to 10 nmol of the semiconductor nanoparticles in terms of anamount of substance as a particle; provided, however, that an amount ofsubstance as a particle is a molar amount when a single particle isregarded as a huge molecule, which is equal to a value obtained bydividing the number of nanoparticles in the dispersion with Avogadro'snumber (N_(A)=6.022×10²³).

In the method of producing core-shell semiconductor nanoparticles,preferably, indium acetate or gallium acetylacetonate is used as a Group13 element source, sulfur in the form of a simple element, thiourea, ordibenzyldisulfide is used as Group 16 element source, and a mixedsolution of oleylamine and dodecanethiol is used as a dispersion to forma shell containing indium sulfide or gallium sulfide.

In the heating up method, when a mixed solution of oleylamine anddodecanethiol is used as a dispersion, the resulting core-shellsemiconductor nanoparticles show an emission spectrum with a broad peakattributable to defect emission with an intensity satisfactory smallerthan the peak intensity of the band edge emission. This tendency is alsosignificantly recognized when gallium source is used as a Group 13element source.

The shell is thus formed to complete core-shell semiconductornanoparticles. The resultant core-shell semiconductor nanoparticles maybe separated from the solvent, and may be further purified and dried asappropriate. The separation, purification and drying methods are asdescribed in relation to the semiconductor nanoparticles, and thus thedetails will not be described.

When the shell semiconductor is essentially composed of Group 1, Group13, and Group 16 elements, the shell can be formed in the same manner asdescribed above. In other words, a Group 1 element-containing compound,a Group 13 element-containing compound, and a Group 16 element in theform of a simple element or a Group 16 element-containing compound areadded to the dispersion containing the core-to-be semiconductornanoparticles to form the shell.

Examples of the Group 1 element-containing compound include organicsalts, inorganic salts, and organic metal compounds of Group 1 elements.Specific examples of the Group 1 element-containing compound includenitrate, acetate, sulfate, hydrochloride, sulfonate, and acetylacetonatecomplexes, and preferable examples include organic salts, such asacetate, or organic metal compounds, because organic salts and organicmetal compounds are highly soluble in an organic solvent, and can allowthe reaction to proceed further uniformly.

When the core-shell semiconductor nanoparticles have their shellsurfaces modified with a specific modifier, the core-shell semiconductornanoparticles obtained above may undergo a modification step. Themodification step causes the core-shell semiconductor nanoparticles anda specific modifier containing phosphorus (P) with a negative oxidationnumber to come into contact with each other to modify the shell surfacesof the core shell particles. This produces semiconductor nanoparticlesthat exhibit a band edge emission with a further improved quantum yield.

The core-shell semiconductor nanoparticles and the specific modifier arecontacted by, for example, mixing a dispersion of the core-shellsemiconductor nanoparticles and the specific modifier. Or, the coreshell particles may be mixed with a specific liquid modifier. Thespecific modifier may be used in the form of its solution. Thedispersion of the core-shell semiconductor nanoparticles is obtained bymixing the core-shell semiconductor nanoparticles with an appropriateorganic solvent. Examples of the organic solvent used for dispersioninclude halogen solvents, such as chloroform; aromatic hydrocarbonsolvents, such as toluene; and aliphatic hydrocarbon solvents, such ascyclohexane, hexane, pentane, and octane. The concentration, in anamount of substance, of the core-shell semiconductor nanoparticles inthe dispersion is, for example, from 1×10⁻⁷ mol/L to 1×10⁻³ mol/L, andpreferably from 1×10⁻⁶ mol/L to 1×10⁻⁴ mol/L. An amount of substance asused herein has the same meaning as the one described in the shellformation.

The amount of the specific modifier to be used relative to thecore-shell semiconductor nanoparticles is, for example, from 1 to 50,000times in molar ratio. When the dispersion of the core-shellsemiconductor nanoparticles has a concentration, in an amount ofsubstance, of the core-shell semiconductor nanoparticles in thedispersion of from 1.0×10⁻⁷ mol/L to 1.0×10⁻³ mol/L, the dispersion andthe specific modifier may be mixed in a volume ratio of from 1:1000 to1000:1.

The temperature at which the core-shell semiconductor nanoparticles andthe specific modifier come in contact is, for example, from −100° C. to100° C. or from −30° C. to 75° C. The duration of contact may beselected as appropriate in accordance with, for example, the amount ofuse of the specific modifier or the concentration of the dispersion. Theduration of contact is, for example, 1 min or more, preferably 1 h ormore, and 100 h or less, preferably 48 h or less. The atmosphere ofcontact is, for example, an atmosphere of an inert gas, such as nitrogengas or a rare gas.

Light-Emitting Device

The light-emitting device according to a third embodiment includes alight conversion member containing the semiconductor nanoparticlesand/or the core-shell semiconductor nanoparticles, and a semiconductorlight-emitting element. In this light-emitting device, for example,emission from the semiconductor light-emitting element is partiallyabsorbed by the semiconductor nanoparticles and/or the core-shellsemiconductor nanoparticles, and light with a further longer wavelengthis emitted. The light from the semiconductor nanoparticles and/or thecore-shell semiconductor nanoparticles and the residual light from thesemiconductor light-emitting element are mixed, and the mixed light maybe used as emission from the light-emitting device.

Specifically, using a semiconductor light-emitting element that emitsbluish-violet light or blue light with a peak wavelength of from about400 nm to about 490 nm, and the semiconductor nanoparticles and/or thecore-shell semiconductor nanoparticles that absorb blue light and emityellow light produces a light-emitting device that emit white light. Or,using two types of the semiconductor nanoparticles and/or the core-shellsemiconductor nanoparticles: those that absorb blue light and emit greenlight and those that absorb blue light and emit red light may alsoproduce a white light-emitting device.

Or, using a semiconductor light-emitting element that emits ultravioletrays having a peak wavelength of 400 nm or less, and three types of thesemiconductor nanoparticles and/or the core-shell semiconductornanoparticles that absorb ultraviolet rays and emit blue light, greenlight, and red light, respectively, can also produce a whitelight-emitting device. In this case, ultraviolet rays emitted from thelight-emitting element are preferably all absorbed by the semiconductornanoparticles and/or the core-shell semiconductor nanoparticles toprevent their leakage outside.

The semiconductor nanoparticles and/or the core-shell semiconductornanoparticles according to the present embodiment may be used incombination with other semiconductor quantum dots, or used incombination with other fluorescent materials (e.g., organic or inorganicfluorescent materials) that are not semiconductor quantum dots. Theother semiconductor quantum dots are, for example, the binarysemiconductor quantum dots described in the section of Description ofthe Related Art. Examples of the fluorescent materials that are notsemiconductor quantum dots include garnet fluorescent materials such asaluminium garnet. Examples of the garnet fluorescent materials includecerium-activated yttrium aluminium garnet fluorescent materials andcerium-activated lutetium aluminium garnet fluorescent materials. Inaddition, europium and/or chromium-activated nitrogen-containing aluminosilicate calcium fluorescent materials, europium-activated silicatefluorescent materials; nitride fluorescent materials, such as β-SiAlONfluorescent materials, CASN or SCASN; rare-earth nitride fluorescentmaterials, such as LnSi₃N₁₁ or LnSiAlON; oxynitride (e.g., BaSi₂O₂N₂:Euor Ba₃Si₆O₁₂N₂:Eu-based) fluorescent materials; sulfide-based (e.g.,CaS, SrGa₂S₄, SrAl₂O₄, and ZnS-based) fluorescent materials;chlorosilicate fluorescent materials; SrLiAl₃N₄:Eu fluorescentmaterials, SrMg₃SiN₄:Eu fluorescent materials; and manganese-activatedfluoride complex fluorescent material, such as K₂SiF₆:Mn fluorescentmaterials may be used.

In the light-emitting device, a light conversion member including thesemiconductor nanoparticles and/or the core-shell semiconductornanoparticles may be, for example, a sheet or plate-like member, or3-dimensional member. An example of the 3-dimensional member is asealing member in a surface mount light emitting diode where asemiconductor light-emitting element is arranged on the bottom surfaceof a recess formed in the package, and resin is filled into the recessto form the sealing member to seal the semiconductor light-emittingelement.

Another example of the light conversion member is found in the casewhere a semiconductor light-emitting element is disposed on a planarsubstrate. In this case, the light conversion member is a resin memberformed in a manner to surround the top surface and the side surfaces ofthe semiconductor light-emitting element with a substantially uniformthickness. Still another example of the light conversion member is foundin the case where a resin member containing a reflective material isfilled around a semiconductor light-emitting element such that the topend of the resin member aligns with the semiconductor light-emittingelement. In this case, the light conversion member is a plate-like resinmember with a given thickness formed on top of the semiconductorlight-emitting element and the resin member containing the reflectivematerial.

The light conversion member may be arranged in contact with thesemiconductor light-emitting element, or apart from the semiconductorlight-emitting element. More specifically, the light conversion membermay be a pellet member, a sheet member, a plate-like member, or arod-like member arranged apart from the semiconductor light-emittingelement, or a member arranged in contact with the semiconductorlight-emitting element, for example, a sealing member, a coating member(a member separately formed from a mold member and covering thelight-emitting element) or a mold member (for example, a lens-shapedmember). When two or more types of the semiconductor nanoparticles orthe core-shell semiconductor nanoparticles according to the presentdisclosure that emit light with different wavelengths are used, the twoor more types of the semiconductor nanoparticles or the core-shellsemiconductor nanoparticles according to the present disclosure may bemixed in a single light conversion member, or two or more lightconversion members each containing only one type of quantum dots may beused in combination. In this case, the two or more light conversionmembers may have a layered structure, or arranged in dot or stripepatterns on a plane surface.

An example of the semiconductor light-emitting element includes an LEDchip. The LED chip may include one, or two or more types ofsemiconductor layers selected from, for example, GaN, GaAs, InGaN,AlInGaP, GaP, SiC, and ZnO. The semiconductor light-emitting elementthat emits bluish-violet light, blue light, or ultraviolet rayspreferably contains a GaN compound semiconductor layer having acomposition represented by, for example, In_(X)Al_(Y)Ga_(1-X-Y)N (where0≤X, 0≤Y, and X+Y<1).

The light-emitting device is preferably incorporated into a liquidcrystal display as a light source. The semiconductor nanoparticlesand/or the core-shell semiconductor nanoparticles according to thepresent disclosure exhibit a band edge emission with a short emissionlifetime. Thus, a light emitting device containing the semiconductornanoparticles and/or the core-shell semiconductor nanoparticles issuitable as a light source for a liquid crystal display that needs arelatively quick response rate. Also, the semiconductor nanoparticlesand/or the core-shell semiconductor nanoparticles according to thepresent disclosure can exhibit a band edge emission having an emissionpeak with a small half bandwidth.

Thus, without using a thick-color filter, a liquid crystal display withgood color reproducibility can be obtained by including a light emittingdevice that includes:

a blue semiconductor light-emitting element that emits blue light with apeak wavelength in the range of from 420 nm to 490 nm, the semiconductornanoparticles and/or the core-shell semiconductor nanoparticlesaccording to the present disclosure that emit green light with a peakwavelength in the range of from 510 nm to 550 nm, and preferably in therange of from 530 nm to 540 nm, and the semiconductor nanoparticlesand/or the core-shell semiconductor nanoparticles according to thepresent disclosure that emit red light with a peak wavelength in therange of from 600 nm to 680 nm, and preferably from 630 nm to 650 nm;or,

a semiconductor light-emitting element that emits an ultraviolet lightwith a peak wavelength of 400 nm or less, and the semiconductornanoparticles and/or the core-shell semiconductor nanoparticlesaccording to the present disclosure that emit blue light with a peakwavelength in the range of from 430 nm to 470 nm, and preferably from440 nm to 460 nm, the semiconductor nanoparticles according to thepresent disclosure that emit green light with a peak wavelength in therange of from 510 nm to 550 nm, and preferably from 530 nm to 540 nm,and the semiconductor nanoparticles and/or the core-shell semiconductornanoparticles according to the present disclosure that emit red lightwith a peak wavelength in the range of from 600 nm to 680 nm, andpreferably from 630 nm to 650 nm.

The light emitting device according to the present embodiment may beused, for example, as a direct backlight, or an edge backlight.

Alternatively, a light conversion member containing the semiconductornanoparticles and/or the core-shell semiconductor nanoparticlesaccording to the present disclosure may be incorporated into a liquidcrystal display in the form of a sheet, a plate, or a rod formed fromresin or glass independent of a light emitting device.

EXAMPLES

The present invention will now be described specifically with referenceto Examples; however, the present invention is not limited to theseExamples.

Example 1

0.1402 mmol of silver acetate (AgOAc), 0.1875 mmol of indium acetate(In(OAc)₃), 0.047 mmol of gallium acetate (Ga(OAc)₃), and 0.3744 mmol ofthiourea, or a sulfur source, were charged and dispersed into a mixedsolution of 0.05 cm³ of 1-dodecanethiol and 2.95 cm³ of oleylamine. Thedispersion was then put into a test tube together with a stirrer, andthe test tube was purged with nitrogen. The contents in the test tubewere then subjected to a first heat-treating step at 150° C. for 10 min,and a second heat-treating step at 250° C. for 10 min while beingstirred in the nitrogen atmosphere. After the heat-treatment, theresultant suspension was allowed to cool, and then centrifuged (radius146 mm, 4000 rpm, 5 min) to collect the supernatant or the dispersion.To this, methanol was added until semiconductor nanoparticles started toprecipitate, and the mixture was centrifuged (radius 146 mm, 4000 rpm, 5min) to allow the semiconductor nanoparticles to precipitate. Theprecipitate was collected and dispersed in chloroform to obtain asemiconductor nanoparticle dispersion. Table 1 shows the initialcomposition of the raw materials.

Examples 2 and 3

A semiconductor nanoparticle dispersion was each obtained in the samemanner as in Example 1 except that the initial compositions of the rawmaterials were changed as shown in Table 1.

TABLE 1 AgOAc In(OAc)₃ Ga(OAc)₃ (NH₂)₂CS (mmol) (mmol) (mmol) (mmol)Example 1 0.1402 0.1875 0.0470 0.3744 Example 2 0.0467 0.0625 0.01560.1250 Example 3 0.0701 0.0938 0.0329 0.1997

Example 4

0.125 mmol of silver acetate (AgOAc), 0.0375 mmol of indiumacetylacetonate (In(CH₃COCHCOCH₃)₃;In(AcAc)₃), 0.0875 mmol of galliumacetylacetonate (Ga(CH₃COCHCOCH₃)₃;Ga(AcAc)₃), and 0.25 mmol of sulfur,or a sulfur source, were charged and dispersed into a mixed solution of0.25 cm³ of 1-dodecanethiol and 2.75 cm³ of oleylamine. The dispersionwas put into a test tube together with a stirrer, and the test tube waspurged with nitrogen. The contents in the test tube were heat-treated at300° C. for 10 min while being stirred in the nitrogen atmosphere. Afterthe heat-treatment, the same after-treatment as in Example 1 was carriedout to obtain a semiconductor nanoparticle dispersion. Table 2 shows theinitial composition of the raw materials.

Examples 5 to 8

A semiconductor nanoparticle dispersion was each obtained in the samemanner as in Example 4 except that the initial composition of the rawmaterials and the heat treatment conditions were changed as shown inTable 2.

Example 9 Preparation of Core Semiconductor Nanoparticles

A core semiconductor nanoparticle dispersion was obtained in the samemanner as above with the initial composition of the raw materials andthe heat treatment conditions shown in Table 2.

Examples 10 and 11 Preparation of Core-Shell Semiconductor Nanoparticles

From the dispersion of the core semiconductor nanoparticles obtained inExample 9, 1.0×10⁻⁵ mmol, which is an amount of substance of thenanoparticles (the number of particles), was weighed, and the solventwas allowed to evaporate in the test tube. 5.33×10⁻⁵ mol of Ga(AcAc)₃(19.3 mg) and of thiourea (2.75 mg) were dispersed in a mixed solvent of2.75 mL of oleylamine and 0.25 mL of dodecanethiol to obtain adispersion. The dispersion was stirred at 300° C. for 120 min in anitrogen atmosphere. This was removed from the heating source, allowedto cool to normal temperature, and then centrifuged (radius 150 mm, 4000rpm, 5 min) to separate the supernatant portion from the precipitateportion. Methanol was then added to each of them to obtain a precipitateof core-shell semiconductor nanoparticles. Each precipitate wascentrifuged (radius 150 mm, 4000 rpm, 5 min) to collect a solidcomponent. Ethanol was further added, and each mixture was centrifugedin the same manner. Those obtained from the supernatant portion and theprecipitate portion were each dispersed in chloroform, and variousmeasurements were carried out. The average particle diameter of theshell-coated particles was measured. The average particle diameter ofthe core shell particles obtained from the precipitate was 4.3 nm, andthe average particle diameter of the particles obtained from thesupernatant portion was 3.5 nm. The difference from the average particlediameter of the core semiconductor nanoparticles shows that the shellhas a thickness in average of about 0.75 nm and 0.35 nm, respectively.The core-shell semiconductor nanoparticle dispersion obtained from thesupernatant portion is hereinafter referred to as Example 10, and thecore-shell semiconductor nanoparticle dispersion obtained from theprecipitate portion is referred to as Example 11.

TABLE 2 Heattreating temperature AgOAc In(AcAc)₃ Ga(AcAc)₃ S (° C.)(mmol) (mmol) (mmol) (mmol) Example 4 300 0.125 0.0375 0.0875 0.25Example 5 280 0.125 0.0375 0.0875 0.25 Example 6 250 0.2 0.08 0.12 0.4Example 7 250 0.1 0.04 0.06 0.2 Example 8 280 0.1 0.04 0.06 0.2 Example9 300 0.125 0.0375 0.0875 0.25

Comparative Example 1

Silver acetate (AgOAc) and indium acetate (In(OAc)₃) were each weighedsuch that Ag/Ag+In is 0.3 (Comparative Example 1), 0.4 (ComparativeExample 3), and 0.5 (Comparative Example 2), and that the sum of the twometal salts was 0.25 mmol. The silver acetate (AgOAc), indium acetate(In(OAc)₃), and 0.25 mmol of thiourea were charged and dispersed in amixed solution of 0.10 cm³ of oleylamine and 2.90 cm³ of1-dodecanethiol. The dispersion was put into a test tube together with astirrer, and the test tube was purged with nitrogen. The contents in thetest tube were subjected to the first heat-treating step at 150° C. for10 min, and then the second heat-treating step at 250° C. for 10 minwhile being stirred in the nitrogen atmosphere. After theheat-treatment, the resultant suspension was allowed to cool, and thencentrifuged (radius 146 mm, 4000 rpm, 5 min) to precipitatesemiconductor nanoparticles.

For Comparative Example 1, the resultant precipitate was washed withmethanol, and to this, chloroform was added and centrifuged (radius 146mm, 4000 rpm, 15 min). The supernatant was collected to obtain asemiconductor nanoparticle dispersion. For Comparative Examples 2 and 3,methanol was added until nanoparticles stated to precipitate in thedispersion, or the supernatant, and centrifuged (radius 146 mm, 4000rpm, 5 min) to precipitate semiconductor nanoparticles. Each precipitatewas taken out, and dispersed in chloroform to obtain a semiconductornanoparticle dispersion.

Composition Analysis

The resultant respective semiconductor nanoparticles were subjected toan X-ray fluorescence analyzer to determine the ratio of Ag, In, Ga, andS atoms contained in the semiconductor nanoparticles when all the numberof atoms were 100, and then Ga ratio calculated by Ga/(Ga+In), Ag ratiocalculated by Ag/(Ag+In+Ga), and S ratio calculated by S/(Ag+In+Ga) weredetermined. Table 3 shows the results.

Average Particle Diameter

The shapes of the resultant semiconductor nanoparticles were observed,and their average particle diameters were measured. The resultantparticles were spherical or polygonal. Table 3 shows the averageparticle diameters.

Light Emission Properties

For the respective semiconductor nanoparticles, the absorption spectrumand the emission spectrum were each measured. The absorption spectrum inthe wavelength range of 190 nm to 1100 nm was measured using a diodearray spectrophotometer (trade name: Agilent 8453A by AgilentTechnologies). The emission spectrum was measured at an excitationwavelength of 365 nm using a multichannel photodetector (trade name:PMA11 by Hamamatsu Photonics). FIG. 1 shows the emission spectra ofExamples 3, 4, and 6, and Comparative Example 3, and FIG. 2 shows theirabsorption spectra. FIG. 4 shows the emission spectra of Examples 10 and11, and FIG. 5 shows their absorption spectra. Table 3 shows the peakemission wavelength of the sharp emission peak (band edge emission) andthe half bandwidth observed in each emission spectrum. Also, the ratioof the band edge emission intensity to the peak emission intensity ofdonor-acceptor pair (DAP) transition (Band edge/DAP) was determined.

X-Ray Analysis Pattern

For the semiconductor nanoparticles obtained in Example 4, the X-rayanalysis (XRD) pattern was determined, and compared with tetragonalcrystal (chalcopyrite) AgInS₂ and orthorhombic crystal AgInS₂. FIG. 3shows the determined XRD pattern. The XRD pattern shows that thesemiconductor nanoparticles of Example 4 have about the same crystalstructure as the tetragonal crystal AgInS₂. The XRD pattern wasdetermined using a powder X-ray diffractometer (trade name: SmartLab) byRigaku.

TABLE 3 DAP Average Band edge transiton particle emission Half emissionAg/ Ga/ S/ diameter wavelength bandwidth Bandedge/ wavelength (Ag + Ga +h) (h + Ga) (Ag + Ga + h) (nm) (nm) (nm) DAP (nm) Example 1  0.12 0.580.76 <10    580  57  2.538 685 Example 2  0.27 0.29 1.14 3.9 580  42 3.674 690 Example 3  0.07 0.71 0.66 <10    575  48  1.97 680 Example 4 0.50 0.63 1.32 2.8 514  44  5.93 600 Example 5  0.46 0.65 1.27 <10   511  46  2.482 607 Example 6  0.36 0.85 0.84 <10    540  48  1.615 680Example 7  0.49 0.52 1.51 <10    513  48  1.561 609 Example 8  0.51 0.531.37 <10    519  55  1.403 638 Example 9  0.48 0.65 1.28 <10    512  45 1.56 611 Example 10 0.42 0.72 1.41 3.5 510  38 14.7  600 Example 110.42 0.73 1.34 4.3 520  38 9.9 600 Comparative 0.43 — 1.24 10.4  — 212 —810 Example 1  Comparative 0.49 — 1.23 3.8 — 172 750 Example 2 Comparative 0.37 — 1.34 4.3 590  47 — 710 Example 3 

Table 3 shows that the semiconductor nanoparticles of the presentembodiments exhibit a band edge emission having a peak emissionwavelength at shorter emission wavelengths than Comparative Example 3.The results of Examples 10 and 11 show that the semiconductornanoparticles having a smaller average particle diameter exhibit a bandedge emission with a shorter emission wavelength even when they areproduced by the same method of producing semiconductor nanoparticles.

Example 12

0.0833 mmol of silver acetate (AgOAc), 0.050 mmol of In(AcAc)₃, 0.075mmol of Ga(AcAc)₃, and 0.229 mmol of sulfur, or a sulfur source, werecharged and dispersed into a mixed solution of 0.25 cm³ of1-dodecanethiol and 2.75 cm³ of oleylamine. The dispersion was then putinto a test tube together with a stirrer, and the test tube was purgedwith nitrogen. The contents in the test tube were then heat-treated at300° C. for 10 min while being stirred in the nitrogen atmosphere. Afterthe heat-treatment, the resultant suspension was allowed to cool, andthen centrifuged (radius 146 mm, 4000 rpm, 5 min) to collect thesupernatant or the dispersion. To this, methanol was added untilsemiconductor nanoparticles started to precipitate, and the mixture wascentrifuged (radius 146 mm, 4000 rpm, 5 min) to precipitate thesemiconductor nanoparticles. The precipitate was collected and dispersedin chloroform to obtain a semiconductor nanoparticle dispersion.

Preparation of Core-Shell Semiconductor Nanoparticles

From the core semiconductor nanoparticle dispersion obtained above,1.0×10⁻⁵ mmol, which is an amount of substance of the nanoparticles (thenumber of particles), was weighed, and the solvent was allowed toevaporate in the test tube. To this, 5.33×10⁻⁵ mol of Ga (AcAc)₃ (19.3mg), 5.33×10⁻⁵ mol of thiourea (2.75 mg), and 2.67×10⁻⁵ mol of lithiumacetate, and 3.0 mL of oleylamine were mixed and dispersed to obtain adispersion. The molar ratio of Li to Ga (Li/Ga) in the dispersion was1/2. The dispersion was then stirred at 300° C. for 15 min in a nitrogenatmosphere. This was removed from the heating source, allowed to cool tonormal temperature, and then centrifuged (radius 150 mm, 4000 rpm, 5min) to separate the supernatant portion from the precipitate portion.Methanol was then added to the supernatant portion to obtain aprecipitate of core-shell semiconductor nanoparticles. The precipitatewas centrifuged (radius 150 mm, 4000 rpm, 5 min) to collect a solidcomponent. Ethanol was further added, and the mixture was centrifuged inthe same manner. The supernatant portion and the precipitate portionwere each dispersed in chloroform, and various measurements were carriedout. The average particle diameter of the shell-coated particles wasmeasured to be 4.7 nm. The difference from the average particle diameterof the core semiconductor nanoparticles shows that the shell each has athickness in average of about 0.75 nm.

For the resultant core-shell semiconductor nanoparticles, thecomposition analysis and determination of the emission spectrum werecarried out in the same manner as described above. Table 4 shows theevaluation results, and FIG. 6 shows its emission spectrum.

Examples 13 to 16

Core-shell semiconductor nanoparticles were prepared in the same manneras in Example 12, with the amounts of Ga(AcAc)₃ and thiourea fixed to5.33×10⁻⁵ mol, except that the molar ratio of Li to Ga (Li/Ga) in thedispersion was changed by changing the amount of addition of lithiumacetate. Table 4 shows the evaluation results, and FIG. 6 shows theiremission spectra.

Examples 17 and 18

Core-shell semiconductor nanoparticles were prepared in the same manneras in Example 12, with the amounts of Ga(AcAc)₃ and thiourea fixed to5.33×10⁻⁵ mol, except that the molar ratio of Li to Ga (Li/Ga) in thedispersion was changed by changing the amount of addition of Ga(AcAc)₃as shown in the table below. Table 4 shows the evaluation results, andFIG. 7 shows their emission spectra.

TABLE 4 Average Band edge particle emission Half Ag/ Ga/ S/ diameterwavelength bandwidth Bandedge/ Li/Ga (Ag + Ga + h) (h + Ga) (g + Ga + h)(nm) (nm) (nm) DAP Example 13  1/10 0.31 0.74 1.25 4.0 530 35 24.286Example 14 1/8 0.30 0.74 1.23 4.2 530 36 25.857 Example 15 1/4 0.25 0.731.20 3.2 530 38 23.375 Example 12 1/2 0.31 0.80 1.08 4.7 528 40 21.875Example 16 1/1 0.29 0.75 1.26 3.2 525 36 39.333 Example 17 2/1 0.35 0.701.18 5.2 517 42 21.000 Example 18 3/2 0.33 0.74 1.13 5.1 517 42 21.750

Containing Li, or a Group 1 element, in the shell reduces DAP emission,or defect emission, and improves the intensity of the band edgeemission. With Ga greater than Li, the band edge emission wavelengthshifts to shorter wavelengths.

Example 19

To the dispersion of the core-shell semiconductor nanoparticles obtainedin Example 12, an approximately the same volume of trioctylphosphine(TOP) was added in a nitrogen atmosphere. This was stirred at roomtemperature for 10 min, and then left standing at room temperature for20 h while being protected from light to obtain a dispersion ofTOP-modified core-shell semiconductor nanoparticles.

For the resultant TOP-modified core-shell semiconductor nanoparticles,the emission spectrum was measured in the same manner as describedabove, and the internal quantum yield was also measured. The core-shellsemiconductor nanoparticles had an internal quantum yield of 13.5%,whereas the TOP-modified core-shell semiconductor nanoparticles had aninternal quantum yield of 31.4%. FIG. 8 shows the emission spectrum.

The disclosures of Japanese Patent Applications No. 2017-037477 (filed:Feb. 28, 2017) and No. 2018-025251 (filed: Feb. 15, 2018) areincorporated herein in their entireties by reference. The literature,patent applications, and technical standards described herein areincorporated herein by reference to the same extent as each of them isspecifically and individually described as being incorporated herein.

What is claimed is: 1-16. (canceled)
 17. Core-shell semiconductornanoparticles, comprising: a core containing Ag, In, Ga, and S; a shellcontaining a Group 13 element and a Group 16 element, wherein thecore-shell semiconductor nanoparticles emit light having an emissionpeak with a wavelength in a range of from 500 nm to less than 590 nm,and a half bandwidth of 70 nm or less upon irradiation of light.
 18. Thecore-shell semiconductor nanoparticles according to claim 17, whereinthe core has a composition of a ratio of the number of Ga atoms to thetotal number of In and Ga atoms being from 0.2 to 0.9.
 19. Thecore-shell semiconductor nanoparticles according to claim 17, whereinthe core has a composition of a ratio of a number of Ag atoms to a totalnumber of Ag, In, and Ga atoms being from 0.05 to 0.55.
 20. Thecore-shell semiconductor nanoparticles according to claim 18, whereinthe core has a composition of a ratio of a number of Ag atoms to a totalnumber of Ag, In, and Ga atoms being from 0.05 to 0.55.
 21. Thecore-shell semiconductor nanoparticles according to claim 17, whereinthe core has a composition of a ratio of the number of Ag atoms to thetotal number of Ag, In, and Ga atoms being from 0.3 to 0.55, and a ratioof the number of Ga atoms to the total number of In and Ga atoms beingfrom 0.5 to 0.9.
 22. The core-shell semiconductor nanoparticlesaccording to claim 17, wherein the core has a composition of a ratio ofthe number of Ag atoms to the total number of Ag, In, and Ga atoms beingfrom 0.05 to 0.27, and a ratio of the number of Ga atoms to the totalnumber of In and Ga atoms being from 0.25 to 0.75.
 23. The core-shellsemiconductor nanoparticles according to claim 17, wherein the shellfurther contains a Group 1 element.
 24. The core-shell semiconductornanoparticles according to claim 17, wherein the shell contains at leastGa as the Group 13 element.
 25. The core-shell semiconductornanoparticles according to claim 17, wherein the shell contains at leastS as the Group 16 element.
 26. The core-shell semiconductornanoparticles according to claim 17, wherein the shell contains asemiconductor having greater band gap energy than the core.